The most important parts is as you say the TFM Coupler, the Rigid Spacer and the Olsson Block. It is a good idea to upgrade the fan shroud also, either to the 2+ one or by printing for example Labern's fan shroud, since that gives you much better part cooling.

You don't really have to change the PT100 and the heater, but the 35W heater is a nice upgrade if you are printing with 0.8mm nozzle and/or high-temp plastics and wants to push the speed a bit, and the PT100 are a little bit more accurate.

I need to adjust my I2K insulator, just open out the bore a bit as I get a small bulge on the end of the filament at the final retraction that won't re-enter on the next print.
I adjust my previous one and it solved the problem.

Well I replaced the heater block, heater, thermocouple and TFT last night.

The old heater block was pretty well worn, very gummed over and ready to be replaced. I had spare parts (dual extruder option kit) and decided to stick to stock parts. I couldn't remove the heater or thermocouple...the screw just wouldn't budge despite heating it up and trying to twist like crazy on the M3 10 screw

I was really puzzled on how to feed the wires out the top of the print head but after re-reading how I had assembled it, removing the top piece made life a lot easier!

I was really careful on the re-assembly and notice there's a angle/slant between the aluminum and wood piece. Despite carefully threading in the 4 rods, it's still there but doesn't seem to affect how things are working.

One nice thing about this process was re-aligning the print head so that the wires are out the back and the wiring is not straining that position.